a) Field of the Invention
This invention relates to an electric vehicle which runs by driving its wheels by an electric drive motor, and especially to a hybrid electric vehicle equipped with a combustion engine for driving a generator to recharge a battery unit or a running combustion engine for driving the wheels.
b) Description of the Related Art
There is an ever-increasing move toward protection of the global environment in recent years. In particular, the pollution of air due to mass consumption of fossil fuel has become a serious problem. Prevention of air pollution is therefore an extremely important theme for the protection of the global environment.
Presently, vehicles with engines relying upon fossil fuel such as gasoline or diesel oil are the main stream. Air pollution by exhaust gas from these vehicles has become an extremely serious problem especially in big cities in particular, in urban districts so that electric vehicles, which are free of exhaust gas, have been given a second look.
At the present stage, however, these electric vehicles still involve various problems which still have to be solved for their practical use. Electric vehicles have therefore not spread broadly to the public although they have been put into practical use in some fields. To make electric vehicles more practical, a variety of techniques has thus been proposed to date.
For example, increasing the distance coverable by a presently-available electric vehicle per a single charging inevitably requires mounting of more batteries because the capacity of each battery is limited. Use of such many batteries, however, leads to a substantial increase in the vehicle weight and also occupation of a large space inside the vehicle, resulting in the inconvenience that the power performance and riding comfort of the vehicle are deteriorated. Use of fewer batteries definitely makes it impossible to increase the distance coverable per charging.
Further, an electric vehicle has to be charged whenever the remaining capacity of its batteries as an energy source is decreased. Currently, however, this battery charging is not so easy as replenishment of gasoline. If an electric vehicle can no longer run due to insufficient battery capacity and stops on the road, it is not easy to bring the vehicle back to a running condition.
With a view to lessening the above-mentioned problems of such currently-available electric vehicles, electric vehicles equipped with an internal combustion engine mounted thereon, that is, so-called hybrid electric vehicles have been proposed.
Specific examples of such hybrid electric vehicles include series hybrid electric vehicles such as that shown in FIG. 8(a) and parallel hybrid electric vehicles such as that illustrated in FIG. 8(b).
The series hybrid electric vehicle shown in FIG. 8(a) is equipped with an internal combustion engine 7 and a generator 6 driven by the internal combustion engine 7, which are both mounted on the vehicle. When the capacity of a battery unit 1 becomes insufficient, the internal combustion engine 7 is operated to produce electric power by the generator 6. While charging the battery unit 1 by the electric power so generated, wheels 3 are driven by a motor 2 to permit running. This allows the electric vehicle to run even when the capacity of the battery unit 1 has become insufficient. Incidentally, FIG. 8(a) also depicts a motor controller 4 and a drive management controller 5. The motor controller 4 controls an output of the motor 2 in accordance with a control signal from the drive management controller 5.
On the other hand, the parallel hybrid electric vehicle illustrated in FIG. 8(b) carries an internal combustion engine 8 in parallel with an electric drive motor 2, so that the internal combustion engine 8 can also drive its associated wheels 3 in addition to or in place of driving the remaining wheels 3 by the electric drive motor 2. The parallel hybrid electric vehicle can therefore run by the internal combustion engine 8 even when the capacity of the battery unit 1 has become insufficient.
These hybrid electric vehicles can each increase its running distance by auxiliary operation of its internal combustion engine 8 while reducing the exhaust gas and the air pollution.
In these hybrid electric vehicles, the battery units inevitably become large, thereby imposing a significant weight load on them.
On the other hand, such hybrid electric vehicles such as mentioned above, can each run by obtaining electric energy from the generator driven by the internal combustion engine and driving the motor with the electric energy (series hybrid electric vehicles) or by directly driving wheels with the internal combustion engine (parallel hybrid electric vehicles). Accordingly, there is the possibility that with a view toward enhancing the running performance of a hybrid electric vehicle, its user may remove the battery unit by himself or may replace the specified battery unit by a battery unit lighter in weight and smaller in capacity than the specified battery unit to reduce the weight of the vehicle.
Advantages of the hybrid electric vehicle may however not be fully appreciated if the hybrid electric vehicle is driven with its,battery unit removed or with its specified battery unit replaced by a battery unit of smaller capacity.
Further, there is the potential problem that the hybrid electric vehicle may be driven more frequently while operating its internal combustion engine. This may hence lead to a failure in fully achieving the protection of the environment, the primary objective of electric vehicles.